Whole Earth Telescope discovery of a strongly distorted quadrupole pulsation in the largest amplitude rapidly oscillating Ap star

Abstract

We present a new analysis of the rapidly oscillating Ap (roAp) star, 2MASS J$19400781-4420093$ (J1940; $V=13.1$). The star was discovered using SuperWASP broadband photometry to have a frequency of 176.39 d${}^{-1}$ (2041.55 $\mu$Hz; $P=8.2$ min; Holdsworth et al. 2014a) and is shown here to have a peak-to-peak amplitude of 34 mmag. J1940 has been observed during three seasons at the South African Astronomical Observatory, and has been the target of a Whole Earth Telescope campaign. The observations reveal that J1940 pulsates in a distorted quadrupole mode with unusual pulsational phase variations. A higher signal-to-noise ratio spectrum has been obtained since J1940's first announcement, which allows us to classify the star as A7 Vp Eu(Cr). The observing campaigns presented here reveal no pulsations other than the initially detected frequency. We model the pulsation in J1940 and conclude that the pulsation is distorted by a magnetic field of strength $1.5$ kG. A difference in the times of rotational maximum light and pulsation maximum suggests a significant offset between the spots and pulsation axis, as can be seen in roAp stars.

arXiv comment14 pages, 16 figures, 12 tables, accepted for publication in MNRAS

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Cited by in corpus (10)

• K2 space photometry reveals rotational modulation and stellar pulsations in chemically peculiar A and B stars
• TESS Cycle 1 observations of roAp stars with 2-min cadence data
• Suppressed phase variations in a high amplitude rapidly oscillating Ap star pulsating in a distorted quadrupole mode
• K2 observations of the rapidly oscillating Ap star 33 Lib (HD 137949): new frequencies and unique non-linear interactions
• LCO observations of a super-critical distorted pulsation in the roAp star J0855 (TYC 2488-1241-1)
• Environmental effects on halo abundance and weak lensing peak statistics toward large underdense regions
• Discovery of multiple p-mode pulsation frequencies in the roAp star, HD 86181
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